Lung diseases that arise from injury to or defective development of the pulmonary epithelium including COPD, emphysema, pulmonary fibrosis, and bronchopulmonary dysplasia cause significant morbidity and mortality. An attractive therapeutic goal would be the reversal of emphysema through regeneration of alveolar septae. However, little is known about the cellular and molecular events that lead to alveolar septation during lung development and lung regeneration. More scientific research is needed to identify the appropriate cells, genes and pathways that need to be stimulated or inhibited to promote alveolar regeneration. While other labs have demonstrated that the interstitial myofibroblast plays an important role during lung development we showed that FGF signaling regulates the differentiation of the myofibroblast during alveolarization and during alveolar regeneration. The proposed research will identify the myofibroblast precursor and define the role of FGF and PDGF signaling in this differentiation process to provide new insights into the role of the myofibroblast during alveolarization and neoalveolarization and enable the development of new strategies to target the appropriate signaling pathway in precursor cells to induce regrowth of new septae. We will test a new conceptual model of alveolar regeneration by using PNX as an experimental tool along with transgenic mouse technology to label lipofibroblasts and follow their differentiation during alveolar development and regeneration and determine the role of FGF and PDGF signaling pathways during myofibroblast differentiation by using transgenic mice and pharmacological reagents to inhibit myofibroblast differentiation. In Aim 1 we will determine the role of the interstitial lipofibroblast during normal alveolarization and neoalveolarization after PNX. Transgenic mice that permanently label lipofibroblasts and their progeny with bgal expression will be used to perform lineage-tracing studies during normal alveolarization and neo-alveolarization after PNX. In Aim 2 we will determine the role of FGF signaling in the differentiation and function of the myofibroblast during neoalveolarization. Using transgenic mice that express a dominant negative FGFR we will perform lineage-tracing studies to determine the cell fate of the lipofibroblast during normal alveolarization and compensatory lung growth; and identify the FGF ligands and receptors that induce (SMA expression in vitro. In Aim 3 we will define the role of FGF and PDGF signaling on elastin synthesis in the differentiating myofibroblast. We will use transgenic mice to inhibit FGF signaling, or a specific PDGFR kinase inhibitor to assess elastic fiber assembly after PNX. The results from the proposed studies will identify the appropriate target cells and relevant signaling pathway that induce alveolar regeneration and help develop new strategies to regenerate alveolar tissue to improve the long-term sequelae of bronchopulmonary dysplasia in children and emphysema in the adult lung with COPD.